JDBC增删改查示例

数据库表

CREATE TABLE `customers` (
`id` int NOT NULL AUTO_INCREMENT,
`name` varchar(15) DEFAULT NULL,
`email` varchar(20) DEFAULT NULL,
`birth` date DEFAULT NULL,
`photo` mediumblob,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=39 DEFAULT CHARSET=gb2312;

引入的依赖下图是为了快速将inputStream转byte[]引入的一个依赖

没有使用连接池

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.30</version>
</dependency>
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.13.2</version>
    <scope>test</scope>
</dependency>

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.11.0</version> <!-- 使用最新版本 -->
</dependency>

封装的工具类,这个工具类如果说想使用泛型需要把除了closed和getConnection的其他几个方法的静态去掉

package com.utils;

import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.ResourceBundle;

/**
 * @author hrui
 * @date 2023/10/16 8:45
 */
//public  class DBUtils2<T> {
public  class DBUtils2 {
    private static ResourceBundle bundle=ResourceBundle.getBundle("jdbc");
    private static String driver=bundle.getString("jdbc.driver");
    private static String url=bundle.getString("jdbc.url");
    private static String username=bundle.getString("jdbc.username");
    private static String password=bundle.getString("jdbc.password");

    static{
        try {
            Class.forName(driver);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

//    private Class<T> clazz;
//
//    {
//        //获取这个类带泛型的父类DBUtils2<某个类>
//        Type genericSuperclass = this.getClass().getGenericSuperclass();
//        ParameterizedType parameterizedType=(ParameterizedType)genericSuperclass;
//        //获取父类泛型
//        Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();
//        clazz=(Class<T>)actualTypeArguments[0];
//    }


    //通用查询多个  添加事务后conn由外部传入,在关闭时候也由外部关闭,不再次方法关闭conn
    public static <T> List<T> selectList(Connection conn,Class<T> clazz, String sql, Object...args){
        PreparedStatement ps=null;
        ResultSet rs=null;

        try {
            ps=conn.prepareStatement(sql);

            for(int i=0;i<args.length;i++){
                ps.setObject(i+1, args[i]);
            }
            rs = ps.executeQuery();
            ResultSetMetaData metaData = rs.getMetaData();
            int columnCount = metaData.getColumnCount();
            List<T> list=new ArrayList<>();
            while(rs.next()){
                T t = clazz.newInstance();
                for(int i=0;i<columnCount;i++){
                    Object object = rs.getObject(i + 1);
                    //String columnName = metaData.getColumnName(i + 1); 这个方法返回实际列名
                    String columnLabel = metaData.getColumnLabel(i + 1);//该方法返回别名,没有别名就返回列名
                    columnLabel = getString(columnLabel);
                    Field field = clazz.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    field.set(t,object);
                }
                list.add(t);
            }
            return list;
        } catch (Exception e) {
            e.printStackTrace();

        }finally {
            DBUtils.closed(null,ps,rs);
        }
        return null;
    }

    private static String getString(String columnLabel) {
        if (columnLabel.contains("_")) {
            StringBuilder result = new StringBuilder();
            boolean convertNextCharToUpperCase = false;
            for (char c : columnLabel.toCharArray()) {
                if (c == '_') {
                    convertNextCharToUpperCase = true;
                } else {
                    if (convertNextCharToUpperCase) {
                        result.append(Character.toUpperCase(c));
                        convertNextCharToUpperCase = false;
                    } else {
                        result.append(c);
                    }
                }
            }
        }
        return columnLabel;
    }

    //通用查询单个  添加事务后conn由外部传入,在关闭时候也由外部关闭,不再次方法关闭conn
    public static <T> T selectOne(Connection conn,Class<T> clazz,String sql,Object...args){

        PreparedStatement ps=null;
        ResultSet rs=null;

        try {

            ps=conn.prepareStatement(sql);

            for(int i=0;i<args.length;i++){
                ps.setObject(i+1, args[i]);
            }
            rs = ps.executeQuery();
            ResultSetMetaData metaData = rs.getMetaData();
            int columnCount = metaData.getColumnCount();
            if(rs.next()){
                T t = clazz.newInstance();
                for(int i=0;i<columnCount;i++){
                    Object object = rs.getObject(i + 1);
                    //System.out.println(object.getClass());
                    String columnLabel = metaData.getColumnLabel(i + 1);
                    columnLabel = getString(columnLabel);
                    Field field = clazz.getDeclaredField(columnLabel);
                    field.setAccessible(true);
                    field.set(t,object);
                }
                return t;
            }
        } catch (Exception e) {
            e.printStackTrace();

        }finally {
            DBUtils.closed(null,ps,rs);
        }
        return null;
    }




    public static Connection getConnection() throws SQLException {
        Connection connection = DriverManager.getConnection(url, username, password);
        return connection;
    }
    //通用增删改方法  添加事务后conn由外部传入,在关闭时候也由外部关闭,不再次方法关闭conn
    public static int update(Connection conn,String sql,Object...args){
        PreparedStatement ps=null;
        int count=0;
        try {
            ps = conn.prepareStatement(sql);
            for(int i=0;i<args.length;i++){
                ps.setObject(i+1, args[i]);
            }
            count = ps.executeUpdate();
            //ps.execute();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            DBUtils.closed(null,ps,null);
        }

        return count;
    }

    //一些特殊查询封装的方法,例如select count(*) from xxx
    public static <E> E getValue(Connection conn,String sql,Object...args){
        PreparedStatement ps=null;
        ResultSet rs=null;
        try {
            ps = conn.prepareStatement(sql);
            for(int i=0;i<args.length;i++){
                ps.setObject(i+1, args[i]);
            }
            rs=ps.executeQuery();
            if(rs.next()){
                return (E)rs.getObject(1);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            DBUtils2.closed(null,ps,rs );
        }
        return null;
    }


    public static void closed(Connection conn, Statement st, ResultSet rs){
        if(rs!=null){
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(st!=null){
            try {
                st.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(conn!=null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

接口

public interface CustomerDao {
    int insertCustomer(Connection conn, Customers cust);

    int deleteCustomerById(Connection conn,Integer id);

    int updateCustomer(Connection conn,Customers cust);

    Customers selectCustomerById(Connection conn,Integer id);

    List<Customers> selectAllCustomers(Connection conn);

    //查询表中由多少条数据 count(*)返回Long
    Long getCount(Connection conn);

    Date getMaxBirth(Connection conn);
}

接口实现类

public class CustomerDaoImpl extends DBUtils2 implements CustomerDao{
    @Override
    public int insertCustomer(Connection conn, Customers cust) {
        String sql="insert into customers(name,email,birth,photo)value(?,?,?,?)";
        int count = update(conn, sql, cust.getName(), cust.getEmail(), cust.getBirth(), cust.getPhoto());
        return count;
    }

    @Override
    public int deleteCustomerById(Connection conn, Integer id) {
        String sql="delete from customers where id=?";
        int count = update(conn, sql, id);
        return count;
    }

    @Override
    public int updateCustomer(Connection conn, Customers cust) {
        String sql="update customers set name=?,email=?,birth=?,photo=? where id=?";
        int count = update(conn, sql, cust.getName(), cust.getEmail(), cust.getBirth(), cust.getPhoto(),cust.getId());
        return count;
    }

    @Override
    public Customers selectCustomerById(Connection conn, Integer id) {
        String sql="select * from customers where id=?";
        Customers customers = selectOne(conn, Customers.class, sql, id);
        return customers;
    }

    @Override
    public List<Customers> selectAllCustomers(Connection conn) {
        String sql="select * from customers";
        List<Customers> list = selectList(conn, Customers.class, sql);
        return list;
    }

    @Override
    public Long getCount(Connection conn) {
        String sql="select count(*) from customers";
        return getValue(conn, sql);
    }

    @Override
    public Date getMaxBirth(Connection conn) {
        String sql="select max(birth) from customers";
        return getValue(conn, sql);
    }
}

测试类

package com.utils;

import org.apache.commons.io.IOUtils;
import org.junit.jupiter.api.Test;


import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Date;
import java.util.List;

/**
 * @author hrui
 * @date 2023/10/16 16:00
 */
public class CustomterDaoImplTest {

    private CustomerDao customerDao=new CustomerDaoImpl();

    @Test
    public void insertCustomerTest(){
        Connection conn=null;
        try {
            conn = DBUtils2.getConnection();
            InputStream inputStream = CustomterDaoImplTest.class.getClassLoader().getResourceAsStream("123.jpg");
            byte[] imageBytes = IOUtils.toByteArray(inputStream);//这个需要引入commons-io
            // 关闭输入流
            inputStream.close();

            Customers cust=new Customers(null,"小白","xiaobai@163.com",new Date(),imageBytes);
            int i = customerDao.insertCustomer(conn, cust);
            System.out.println(i==1?"新增成功":"新增失败");
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            DBUtils2.closed(conn,null,null);
        }
    }
    @Test
    public void deleteCustomerByIdTest(){
        Connection conn=null;
        try {
            conn = DBUtils2.getConnection();
            int i = customerDao.deleteCustomerById(conn, 1);
            System.out.println(i==1?"删除成功":"删除失败");
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            DBUtils2.closed(conn,null,null);
        }
    };
    @Test
    public void updateCustomer(){
        Connection conn=null;
        try {
            conn = DBUtils2.getConnection();
            InputStream inputStream = CustomterDaoImplTest.class.getClassLoader().getResourceAsStream("123.jpg");
            byte[] imageBytes = IOUtils.toByteArray(inputStream);//这个需要引入commons-io
            // 关闭输入流
            inputStream.close();
            Customers cust=new Customers(2,"王菲菲","feifei@666.com",new Date(),imageBytes);

            int i = customerDao.updateCustomer(conn,cust);
            System.out.println(i==1?"更新成功":"更新失败");
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            DBUtils2.closed(conn,null,null);
        }
    };
    @Test
    public void selectCustomerById(){
        Connection conn=null;
        try {
            conn = DBUtils2.getConnection();
            Customers customers = customerDao.selectCustomerById(conn, 2);
            System.out.println(customers);
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            DBUtils2.closed(conn,null,null);
        }
    };
    @Test
    public void selectAllCustomersTest(){
        Connection conn=null;
        try {
            conn = DBUtils2.getConnection();
            List<Customers> customers = customerDao.selectAllCustomers(conn);
            System.out.println(customers);
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            DBUtils2.closed(conn,null,null);
        }
    };
    @Test
    //查询表中由多少条数据 count(*)返回Long
    public void getCount(){
        Connection conn=null;
        try {
            conn = DBUtils2.getConnection();
            Long count = customerDao.getCount(conn);
            System.out.println(count);
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            DBUtils2.closed(conn,null,null);
        }
    };
    @Test
    public void getMaxBirth(){
        Connection conn=null;
        try {
            conn = DBUtils2.getConnection();
            Date maxBirth = customerDao.getMaxBirth(conn);
            System.out.println(maxBirth);
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            DBUtils2.closed(conn,null,null);
        }
    };
}